We investigated the effects of interleukin-2, which stimulates the proliferation and maturation of thymus-derived lymphocytes, on hypertension and organ injuries in genetically hypertensive rats. Interleukin-2 (5×104 U/kg body wt) was subcutaneously injected into Dahl salt-sensitive rats fed a 4% NaG diet and spontaneously hypertensive rats once a week for 10 weeks. The effects on blood pressure, cardiovascular hypertrophy, and renal function were evaluated. Interleukin-2 treatment lowered blood pressure in Dahl salt-sensitive rats (162 versus 187 mm Hg, P<.005). This antihypertensive effect was associated with an increase in glomerular filtration rate (589 versus 428 mL/d per 100 g body weight, P<.005) and reduction in cardiac weight (268 versus 305 mg/100 g body weight, P<.05). Interleukin-2 also alleviated the marked glomerular sclerosis in Dahl salt-sensitive rats (glomerular injury score, 151 versus 220; P<.001). In contrast, interleukin-2 did not affect the development of hypertension or organ injuries in spontaneously hypertensive rats. Histologically, glomerular and arterial lesions of the kidney were much less marked in spontaneously hypertensive rats than in Dahl salt-sensitive rats. These data indicate that interleukin-2 ameliorates the development of hypertension and cardiac and renal injuries in Dahl salt-sensitive rats.